The present invention relates to a data-base generation management technique, and, particularly, relates to a data-base generation information management method and system in which generation information is acquired by designation in a dictionary device to thereby select a storage corresponding to the level of the generation information or select an extracting means corresponding to the level of the generation information.
The necessity of managing generation information in a data base has become important with the advance of increase in scale of the data base and with the advance of diversification of the data base. In general, generation information becomes massive according to the unit for acquirement thereof. Accordingly, it is necessary to manage generation information efficiently.
In a conventional data-base system, a user application program issues a processing request using a data description language to a data base which is connected under a data-base management system (DBMS). In the conventional system, the DBMS includes a dictionary device for updating or sending out generation management information. Accordingly, generation management information must be indirectly updated or designated through starting the dictionary device according to the request from the application program. In other words, the user could not directly update or designate generation management information. In general, time-series data caused by updating are stored and managed over a plurality of generations in order to protect periodically updated data sets, that is, data files, from destruction caused by a disaster, an accident or an operation error or make the data recoverable. This management is called "generation management". The time-series data are called "generation information". For the double purpose of storage and management, a generation number is given to each generation in a generation data set group by using a catalogue management function of an operating system (OS). The generation number is classified into two, namely, the absolute generation and version number and the relative generation number, as shown, by way of example, in the type VOS3 of Hitachi's OS.
As a conventional generation information management method, a time-series data file management type method in which data are managed by means of "wrap around" using both a time-series data acquirement time and a predetermined acquirement interval decided in advance is described in JP-A-61-243541. Assuming now that the initial time of acquirement of a time-series data is replaced by T.sub.0 and that data are successively acquired at an acquirement interval t.sub.0, the number N of a data acquired at an arbitrary time T.sub.i is calculated by the formula N=(T.sub.i -T.sub.0)/t.sub.0. Accordingly, the time-series data at a desired time can be picked up from the data base exactly and rapidly by providing a base time designating device, a time-to-number converter and a divider.
In the conventional method disclosed in the above Publication, the management method is carried out logically in a program. There arises a problem in that once designated numerical parameters for time and interval cannot be changed with no modification of the program. In short, the time-series data (generation information) must be picked up at a predetermined interval. Further, the factors for generation management, such as an interval, a storage position, an integral effective period and the like, are fixed to constant values, respectively. Accordingly, waiting for a predetermined interval is required for picking up data, so that the data cannot be picked up at an arbitrary time correspondingly to the necessity. In addition, the acquirement method corresponding to the level of the data as to whether or not the data is to be seen soon cannot be provided.